PWM Dimming

PWM dimming control can be realized by applying PWM dim-

ming signal to the DIM terminal of the board directly. When

the DIM pin is pulled to logic high, all output channles are

enabled. When the DIM pin is pulled to logic low (GND), all

output channels are turned OFF. In cascade operation, the

DIM signal should apply to the MASTER unit only. The

LM3464 on the MASTER unit propagates the PWM dimming

signal on its DIM pin to the slave units one by one through the

SYNC pin. PWM dimming control is allowed when thermal

foldback control is activated. When PWM dimming and ther-

mal foldback controls are required simultaneously, the PWM

dimming frequency should be set at least ten times below the

thermal foldback dimming frequency. The thermal foldback

dimming signal reduced the LED currents according to the

voltage level of the Thermal pin when the signal at the DIM

pin is ‘high’ as shown in figure 7.

30127115

FIGURE 7. Thermal Foldback + PWM Dimming Control

9

www.national.com